1. Field of the Invention
This invention relates to an apparatus for adding grinding media to a grinding mill.
2. Description of Related Art
As commonly known, grinding mills are used to reduce the size of solid materials in a mineral processing plant such that they are amenable to further processing, for example, froth flotation. This size reduction is accomplished by means of apparatus which are found in industrial applications such as ball mills, rod mills, pebble mills, etc. The typical grinding mill with which the present invention is concerned is the ball mill and the present invention relates more particularly to a feeder for controlling the feed of the media to the mill. It is not uncommon that a ball mill may use a recipe of balls of different size or operate with non-spherical media which replaces the ball. The alternative media may be in the form of a cylinder, cone or variations of the two.
The conventional methods of feeding the grinding media to ball mills include:
1. The transport of balls by wheelbarrow or manually operated conveyance to a point at which the media may be fed through a chute or pipe by hand or, alternatively, shovelled or dumped from the wheelbarrow into the mill;
2. The transport of the media from a bulk storage facility by a special bottom dump bucket carried by a crane to a chute so arranged that, as the bottom dump bucket is lowered onto the chute, the bucket opens to discharge the entire contents of the bucket through the chute into the grinding mill;
3. The same as 2 above except the media is dumped into a day bin or hopper which may have a capacity of several bucket loads. From this day bin, a gate is opened periodically to allow an operator's estimate of the appropriate amount to run through chute work into the grinding mill;
4. Some feeders do exist which are mounted in the discharge piping from the day bin and comprise a steel drum in the surface of which are located pockets of appropriate size to accept one ball. When the drum is rotated, the balls are lifted over the top of the drum and dropped into the downstream side of the pipe in which the drum is mounted.
The problems associated with these methods of feeding media are respectively:
1. In small mills, hand feeding may be effective but it is a daily task performed on an intermittent basis;
2. Dumping full bucket loads of media into a mill causes a sharp rise in power draft which forms a cycle equivalent to the frequency of media addition. The frequency of media addition can also be made irregular due to erratic availability of a crane and the work forces used to do the job;
3. Similar problems exist when feeding is done from the day bin except that greater latitude is available for crane use due to the reserve attained in the bin. However, the same problems of cyclic power draft result from massive addition of media at any one time.
4. The feeder described is usable only on spherical shaped media of a specific size. It in no way causes the media to dislodge from the day bin if the media hangs up, nor can it handle media of any dimension other than a sphere of a specific size.